Thermopile



Feb. 17. 1925.

WITNESS Filed Aug. 9, 1921 INVENTOR ATTORNEYS Patented Feb. 17, 1925.

HARRY A. MULVANY AND HARRY E. KENNEDY, vOF BERKELEY, CALIFORNIA, AS-

SIGNORS 'I'O PACIFIC FIRE EXTINGUISHER COMPANY, OF SAN FRANCISCO, CALI- FORNIA,'A CORPORATION OF CALIFORNIA.

THERMOPILE.

Application filed August 9, 1921. Serial No. 490,822.

To all whom it may concern:

Be it known that we, HARRY A. MULYANY and HARRY E. KENNEDY, citizens of the United States of America, and residents of Berkeley, county of Alameda, and State of California, have invented a new and useful Thermopile, of which the following is a specification.

Our invention relates to thermopiles. The broad purpose of our invention is the provision of a thermopile having the usual or better than the usual thermal and electrical characteristics and which in addition is possessed of great mechanical strength. Another object of the invention is the provision of a thermopile capable of being manufactured cheaply, and in which the elements of uncertainty in the junction are eliminated.

Our invention possesses other objects and features of advantage, some of which, with the foregoing, will be set-forth in the fol lowing description of our invention. It is to be understood that we do not limit ourselves to the showing made by the said description, as we may adopt variant forms of our invention within the scope of the claims.

In the drawings, Fig. 1 is a vertical sec-' tional view taken longitudinally thru the center of the complete thermopile. .Fig. 2 is a vertical sectional view, the plane of section being indicated by the line 2-2 of Fig. 1. Fig. 3 is a perspective view of the thermo-elect-ric element dissociated from its mounting.

Thermopiles' in use at the present time are chiefly characterized by liability to mechanical injury because of their fragile nature, imperfections in the junctions due to the difiiculty of uniting. the elements. high cost of manufacture because of the great amount of hand work which must be done, and relatively high cost of material comprised in the couples. We have obviated all of these difiiculties and objections in our thermopile, which comprises alternate strips of iron 2 and nickel-copper alloy 3 arranged in zigzag formation as best shown in Fig. 3. The junctions 4 and 5 are formed by fusing the contiguous ends of the strips together 1n a weld. In the drawings the size as well as the spread of the elements of each couple are exaggerated in order to make the construction cearer. The oxide naturally forming on the metal of the couples provides sufficient insulation as between members of the couple but if desired the zigzag strips may be immersed in enamel to provide insulation. Because of the zigzag formation it is possible to make the thermopile with a very large number of couples without exceeding the dimensional limits imposed by other conditions of installation, and because of this fact our thermopile may be installed in the standard outlet. Since theE. M. F. of the thermopile is directly proportional to the number of couples it follows that thermopiles in accordance with our invention may be made of any desired capacity, of course, however, within limits inherent in such devices.

\Ve have found that strips of iron and of nickel-copper alloy of one hundredth of an inch thick, one-quarter inch wide, and about one-half inch long are satisfactory for our purposes. These materials are common and relatively cheap. and welding them together in the form shown presents no unusual difficulties and may be rapidly and economically done, the finished product having perfect "junctions and being substantially immune to injury.

We mount the active element of our thermopile in a block 6 in one face of which a recess is formed. The zigzag strip 2--3 is arranged in the recess, its ends being suitably connected to the conductors 7 and 8 with which it is in circuit. The recess is then filled with plaster of Paris 9' or other suitable material to thermally insulate the enclosed portions of each couple. The proportions are such that about one-half of each couple is buried in the recess, the other half pro ecting from the face of the block. So formed, our thermopile is of the compensating type, that is to say it becomes operative or responsive to the rate of temperature change rather than to temperature rising to a fixed point. In the thermopile we have shown, which is primarily used as a detector in fire alarm systems, a rise of. temperature of six degrees per minute will generate current sufiicient to operate the relay.

Since the operation of the thermopile depends on the difference in temperature beprovide means 'for preventing the operation of the thermopile in such 'momentary fluctuations of temperature. We accomplish this by providing a hood 10 preferably ofcopper which is assembled on the block 6 overthe projecting ends of the couples. The

hood protects the couples from sudden changes of temperature but if such temperature change is prolonged, the hood itself becomes heated and affects the exposed junction by its radiation of heat, whereupon the fiow'of current is induced. Preferably the hood is secured to the block by vthe same screws 11 with which the block is fastened to the wall, or any other suitable fastening means may be provided.

changes in the surrounding atmosphere comprising means for embedding some oi the junction points while leaving the others exposed, and means for fected by momentary changes in the temperature of the surrounding atmosphere.

2. A thermopile comprising a series of alternate strips of disimilar metals joined together, some of the junction points being exposed so as to be afiected by temperature changes, and a hood of good thermal conductivity surrounding the exposed joints but out of contact therewith.

In testimony whereof, we have hereunto set our hands.

HARRY A. MULVANY. HARRY E. KENNEDY.

venting the ex-- "posed junctions from being materially af- 

